Plastic tub wall alignment for dishwashing rack mounting

ABSTRACT

The sidewalls of a front loading, unipartite dishwasher tub molding are necessarily formed with a rearward draft to permit part removal from the forming mold core section. The disclosure is directed to a dishwasher assemblage wherein the forward portions of the rearwardly drafted sidewalls are deformed into parallelism by clamping the same into backing relation with the upright legs of a tub support frame whereby tandem roller pairs may be anchored to the upright legs for the cantilever support of parallel, dishwasher rack supporting tracks.

United States Patent 1 [1 1 34,784 Butsch Sept. 10, 1974 PLASTIC TUB WALL ALIGNMENT FOR DISHWASHING RACK MOUNTING Primary Examiner-Bobby R. Gay Assistant ExaminerWilliam E. Lyddane Attorney, Agent, or Firm-Francis H. Boos [5 7] ABSTRACT The sidewalls of a front loading, unipartite dishwasher tub molding are necessarily formed with a rearward draft to permit part removal from the forming mold core section.

The disclosure is directed to a dishwasher assemblage wherein the forward portions of the rearwardly drafted sidewalls are deformed into parallelism by clamping the same into backing relation with the upright legs of a tub support frame whereby tandem roller pairs may be anchored to the upright legs for the cantilever support of parallel, dishwasher rack supporting tracks.

4 Claims, 3 Drawing Figures u uns---" PLASTIC TUB WALL ALIGNMENT FOR DISHWASHING RACK MOUNTING BACKGROUND OF THE INVENTION The invention is directed to large capacity front loading dishwashers of the type normally comprising a permanent installation and employing upper and lower dish supporting racks as opposed to the smaller, low capacity, portable and/or top loading dishwashers. The reason for the distinction is that the ultimate objective of the invention is the employment of a unipartite plastic tub in large capacity, front loading dishwashers and while some of the problems presented by a proposed use of such a tub would be common to dishwashers of either type; the majority are distinct. Typical distinctions relate to increasing wall flexibility with increasing area, the absence of encompassing metal housings,

greater tub shape complexity and additional interior tub mountings such as dual rack support structures. Accordingly, the ensuing background discussion relates primarily to front loading dishwashers of the type normally adapted for a permanent, under cabinet, installation.

The high temperature, corrosive environment to which automatic dishwasher chambers are subjected dictates that the surfaces of those internal components in contact with such environment be either highly resistant, or immune, to corrosion. Corrosion resistant metals such as stainless steel represent a substantial cost factor in this highly competitive appliance field and the long term industry trend has been toward the use of inert materials to resist the corrosive effects of the chamber environment which are magnified adjacent the usual metal tub seam welds. Insofar as the tub itself, representing the far greater internal surface area exposure, is concerned; the general trend in the United States has been toward the application of an adherent plastic coating to the tub interior while European manufacturers have gone more to the use of plastic tub liners. In either event, the basic structural and design parameters that have prevailed since the advent of the modern front loading automatic dishwasher remained valid. This for the reason that overall dishwasher design parameters, both as regards utility and structural integrity, are virtually unaffected by whether the conventional metal tub is coated, lined or exposed.

conceptually, the use of a unipartite plastic dishwasher tub, i.e., one not requiring a more rigid backing or outer support structure, represents a substantial advance in the art. Exemplary are the greatly decreased cost factors of a molded plastic tub vis-a-vis that of a metal tub requiring a further coating or lining operation; reduction in finishing labor requirements and particularly tub welding operations; longer tub life due to corrosion resistance which is independent of faulty coating procedures or chipping; decreased thermal and acoustical transmission thus minimizing the need for separate insulation; and a lesser inventory requirement for separable components susceptible of integral molding with the tub.

The reduction to practice of such a concept, as applied to front loading dishwashers on an assembly line basis, however, presents a myriad of problems which arise as a requirement for different approaches to those engineering considerations which had previously been predicated upon the use of a metal tub. The distinctions are primarily-those associated with material strength, the unusually high temperature environment to which the tub is subjected and considerations relating to plastic molding procedures. Thus, while the structural integrity of a metallic box beam shape defined by the conventional front loading tub is more than sufficient to resist excessive wall deformation as a function of normal loading forces as during installation, adjustment or use and temperature variations from room ambient to approximately 255F.; such normally applied loading forces would, in the absence of appropriate compensating structure, produce unacceptable wall deformation in a like configured plastic tub. The use of strand-like reinforcing fillers such as fiber glass would, seemingly, ameliorate the overall problem of wall deformation. In actuality, however, the presence of such reinforcing fibers not only effect tub discoloration as discussed below, but their random distribution precludes an accurate prediction of thermal growth characteristics which is an essential parameter in the design of various of the necessary compensating structure. Similarly, impact strength is normally of little moment in the design and installation of metallic tubs but is a matter of major concern in plastic tub design. Furthermore, various structural features appearing in a formed plastic tub as an incident to the forming operation create problems not previously associated with metal tub fabrication. Exemplary of the latter distinction are the presence, on the finished product, of mold lines and/or mold retention ribs creating localized areas of decreased impact resistance as well as the usual wall draft to permit re moval of the product, or tub, from the forming mold. One primary disadvantage arising from this necessary wall draft, and to which the present invention is directed, concerns the mounting of the upper dishwasher rack supporting tracks in parallel.

In addition to the foregoing considerations which relate primarily to mounting and/or assembly procedures for large capacity front loading machines, the desirability of precluding tub discoloration and the desirability for firewall separation of the tub and those electrical components constituting a fire hazard are common to all automatic dishwashing machines. As regards plastic tub discoloration, it is preferred to avoid the use of certain conventional strand type reinforcing fillers, such as chopped strand fiber glass, for the reason that their intersection with the interior plastic surface may provide a bleed path for food stains to permeate the tub structure.

The prior art suggestions relating to the use of small capacity plastic tubs of the top loading type, as in US. Pat. No. 2,691,986 and the use of separate plastic tub components, as in US. Pat. Nos. 2,877,778 and 3,386,306 offer little in the way of guidelines as regards a practical reduction to practice of a large capacity front loading tub for the reason that most of the problems requiring solution are not present in smaller and- /or top loading units and particularly those which employ an enveloping metal housing.

The present invention is concerned with details of the upper dishwasher rack mounting to compensate for the rearwardly drafted tub sidewalls while other of the aforementioned matters are more fully described and claimed in the following, commonly owned, copending applications:

Ser. No. 319,556, filed Dec. 29, 1972, for Double,

Reversed Mounting Boss for Plastic Tubs;

Ser. No. 319,201, filed Dec. 29, 1972, for Fill Funnel Construction for Plastic Tubs;

Ser. No. 319,555, filed Dec. 29, 1972, for Thermal Growth Compensation and Mounting for Plastic Dishwasher Tubs;

Ser. No. 319,202, filed Dec. 29, 1972, for Radiused Mold Walls for Plastic Tubs;

Ser. No. 317,368, filed Dec. 22, 1972, for Angled Levelling Foot for Domestic Appliance;

Ser. No. 319,200, filed Dec. 29, 1972, for Torsionally Reinforced, Skeletal Support Frame for Plastic Tubs;

Ser. No. 319,557, filed Dec. 29, 1972, for Impact Protection for Plastic Tub Employing Mold Retention Ribs;

Ser. No. 319,348, filed Dec. 29, 1972, for Unit- Handled Roller Assembly for Plastic Tub;

Ser. No. 319,203, filed Dec. 29, 1972, for Front Loading Dishwasher Employing Plastic Tub Construction.

Elimination of the conventional front loading metal tub and the substitution therefor of a plastic tub necessitates the presence of mounting and/or support structure to compensate for those inherent characteristics previously available in the use of a metal tub which include a modulus of rigidity sufficient to preclude wall deformation and provide secure anchor points for component mountings, and whose box beam tub shape may be of welded multipart construction to define parallel walls and insure adequate resistance to external loading forces. It is apparent that if the advantages of the invention, as regards decreased cost and weight, are to be retained the necessary mounting and support structure must not, in effect, comprise a confining tub support housing. Rather, a purpose of the invention is to provide an operative, front loading dishwasher unit having a plastic tub whose outer walls comprise the great majority of the outer dishwasher unit construction and would actually be exposed to view prior to installation of the dishwasher unit within an outer decorative housing, which decorative housing may comprise a free standing, portable unit or a permanent undercabinet installation.

SUMMARY OF THE INVENTION It has been found that the requisite structural integrity can be imparted to the overall dishwasher and tub construction through the use of a metal base assembly and a relatively narrow (as compared to the tub depth) metal collar upstanding from the base assembly and extending across the top and sidewalls of the tub immediately adjacent the open end thereof. The front, open end of the tub is then secured to the surrounding, composite box beam collar and base assembly thus anchoring the open end of the tub to a relatively rigid metal shape. The savings in fabrication cost and weight involved in bending a narrow metal strap into an approximate U-shape to form a collar and then joining the same to a base assembly as compared with the utilization of a complex metal shape to either form the tub or envelope a tub liner are obvious.

In addition to an obvious tub support role, the base assembly is designed to perform the dual function of supporting the power operated equipment and provid-' ing a nonflammable firewall between the equipment and the tub.

The tub itself is a unipartite, injection molded tub which is homogeneous throughout and thus exhibits no surface exposed, reinforcing fibers along which food stains could permeate the tub structure. More specifically, the tub is comprised of a homogeneous, unipartite, polypropylene based plastic.

In front loading dishwashers of the type herein disclosed, upper rack loads of 40 pounds are common as is multiple daily usage over an expected dishwasher and tub lifetime in excess of ten years. It is thus apparent that the tub walls, per se, having an exemplary wall thickness of less than 0.2 inch cannot be expected to support the upper rack mounting tracks both by reason of wall deformation under such loads and inherent cold flow characteristics. As regards the latter, reference is had to the presence of track and/0r roller mounting bores which, if supported solely by the plastic sidewalls, would fish tail or enlarge under repeated loading and impact.

Intereference between the upper dishwasher rack and rearwardly drafted tub sidewalls is avoided and the problem of mounting bore enlargement and wall deformation are accommodated by deforming those forward portions of the tub sidewalls, to which the rack supporting rollers are mounted, into substantial parallelism in backing engagement with a metal tub mounting collar which provides roller support anchorage and parallel backing supports to which the forward portions of the tub sidewalls are clamped.

The fact of the rearwardly drafted tub sidewalls is an inherent characteristic of the one piece molding construction to permit part removal from the forming mold. This, broadly for the reason that the multipart, contractible mold core used to form the tub is contracted vertically to clear the lower mold part from the complex bottom configuration while the transverse dimensions of the tub forming mold core remain constant throughout formation and removal of the tub. Thus the mold core sides used to form the tub sidewalls do not contract and product removal takes place through the surface to surface sliding contact between the tub sidewalls and mold core rendering impractical the integral formation of planar, parallel sidewalls. As to the remaining tub walls, i.e., the lower, top and back walls, product removal does not involve sliding surface to surface contact inconsistent with the formation of undrafted walls.

Although it is thought that for the purposes of the present invention; the foregoing brief description of the reasons why the tub sidewalls are drafted rearwardly while the remainder of the tub walls are not will suffice; reference may be had to the aforementioned copending application Ser. No. 319,202 for a more complete description of the molding procedures.

DESCRIPTION OF THE DRAWING FIG. 1 is a broken perspective view of a front loading dishwasher employing a plastic tub;

FIG. 2 is a sectional view taken along line 2-2 of FIG. 1; and

FIG. 3 is a horizontal section of the plastictub taken parallel to the lower tub wall and illustrating the front to rear sidewall draft.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 11 is illustrated a front loading dishwasher 10 including a metal support frame 12 comprised of a base assembly 14 and a tub mounting collar 16 on which is supported a homogeneous, unipartite, plastic tub 18 as well as the remainder of the usual dishwasher components.

The tub sidewalls 20 are preformed with a front to rear draft, as a necessary incident of the one piece molding operation; as best illustrated in FIGS. 2 and 3. The presence of even a minimal draft as on the order of /2"-1 is, of course, inconsistent with the use of the rearwardly convergent sidewalls to locate the necessary parallel mounting of the upper dish rack supporting tracks 22.

Accordingly, in line with the present invention, the forward end portion 24 of the sidewalls 20 are deformed outwardly into substantial parallelism and in backing engagement with the opposed upstanding legs 26 of mounting collar 16. Track supporting roller assemblies 28 may then be mounted to the parallel sidewall portions 24 and anchored in legs 26 for the parallel, cantilever support of tracks 22 from the relatively narrow mounting collar legs whose leading and trailing portions 30, 32 are spaced apart a distance representing a minor fraction of the tub depth. It is, of course, apparent that the roller assembly mounting must position each individual track supporting roller 34 in spaced relation to the inner sidewall surface so that the innermost convergence of sidewalls 20 at their merger with rear tub wall 36lie outside the spaced parallel planes occupied by tracks 22. This relationship is best shown in FIG. 2 where the spacing of rollers 34 from sidewall portions 24 exceeds the maximum sidewall draft indicated between the phantom lines in FIG. 3.

Although the same result of positioning the tracks 22 for non-interferring movement of the upper dishwasher rack could be achieved by simply extending the rearward roller mounting assemblies through an opening in the tub sidewalls and into anchored engagement with the mounting collar without deforming the tub sidewalls; tub integrity would be lost almost immediately as a result of relative movement between the tub sidewalls and roller mounting assemblies producing an enlargement of the mounting bore openings in the plastic sidewalls. Thus with the plastic sidewalls clamped to the mounting collar legs as in FIG. 2, normal dishwasher operation does not produce relative movement between the tub wall and roller mounting assembly as would otherwise be the case with a concomitant coldflow enlargement of tub mounting bores and loss of seal integrity. I

The details of the roller assembly mountings are best shown in FIG. 2 wherein the deformation of tub wall portion 24 is effected by clamping the same against the leading and trailing edge portions of legs 26 through the intermediary of roller mounting flanges 38, mounting collar channels 40 and stressed fasteners 42.

In a preferred form of the invention; the roller mounting assembly performs the dual function of deforming the tub sidewall portion 24 into parallelism and supporting the roller although separate and/or additional stressed fasteners may be used to deform the forward sidewall portions 24, if desired. 4

While the background discussion of this specification is related primarily to front-loading dishwashers of the type normally adapted for a permanent undercounter installation as opposed to the type of dishwasher having a hinged top closure for top-loading, it should be emphasized that many such machines are commercially produced and purchased for indefinite use as a freestanding model adaptable at a later time by the owner to a built-in unit beneath a kitchen countertop to blend with the matching cabinet structure of the kitchen. Generally, the difference between the unit designed as a convertible and the unit to be immediately permanently installed is the inclusion of side, rear and top cabinet appearance panels to the basic unit structure as designed for permanent installation. Therefore, it should be understood that the present invention is specifically directed to the front-loading type of dishwasher structure whether of the generally lower-cost unit having no appearance cabinet enclosure or the more elaborate, temporarily portable unit designed for later modification for use in a fixed location.

I claim:

1. In a front loading dishwasher having a plastic tub of generally rectangular cross-section and preformed to include a top, a bottom and unstressed sidewalls rearwardly convergent from the open front end thereof; a metal tub support frame including upstanding legs en gaging forward end portions of said tub sidewalls in backing relation thereto; each of said legs including coplanar leading edge and trailing edge portions, said legs having a depth constituting a minor fraction of the tub depth; roller mounting assembly means deforming said forward end portions of said plastic tub sidewalls into substantially parallel planes, each roller mounting assembly means in backing engagement with a leg for the parallel cantilever support of upper rack supporting track means, said roller mounting assembly means comprising stressed securing means interconnecting said upstanding legs and tub sidewalls; and upper rack supporting rollers mounted on said securing means and supported in spaced relation to the inner surfaces of said deformed forward end portions of said tub sidewalls to support the track means, said stressed securing means, by interconnecting said upstanding legs and tub sidewalls, preventing normal dishwasher operation from producing a relative movement between said tub sidewalls and said roller mounting assembly means, thereby preventing cold flow enlargement of tub mounting bores and loss of seal integrity.

2. The dishwasher of claim 1 wherein the rearward portions of said tub sidewalls converge rearwardly and merge with the rear tub wall at locations outside the parallel path of upper track movement.

3. The dishwasher of claim 1 wherein said upper rack supporting rollers include mounting flanges associated therewith and abutting said plastic tub sidewalls when said rollers are mounted on said securing means.

4. The dishwasher of claim 3 including mounting collar channels abutting each of said leading and trailing edge portions of said legs outside said dishwasher tub and having said stressed securing means passing therethrough to give additional support to said legs and to said tub sidewall and to coact against said mounting flanges when said stressed securing means are passed therethrough in assembled relation. 

1. In a front loading dishwasher having a plastic tub of generally rectangular cross-section and preformed to include a top, a bottom and unstressed sidewalls rearwardly convergent from the open front end thereof; a metal tub support frame including upstanding legs engaging forward end portions of said tub sidewalls in backing relation thereto; each of said legs including coplanar leading edge and trailing edge portions, said legs having a depth constituting a minor fraction of the tub depth; roller mounting assembly means deforming said forward end portions of said plastic tub sidewalls into substantially parallel planes, each roller mounting assembly means in backing engagement with a leg for the parallel cantilever support of upper rack supporting track means, said roller mounting assembly means comprising stressed securing means interconnecting said upstanding legs and tub sidewalls; and upper rack supporting rollers mounted on said securing means and supported in spaced relation to the inner surfaces of said deformed forward end portions of said tub sidewalls to support the track meaNs, said stressed securing means, by interconnecting said upstanding legs and tub sidewalls, preventing normal dishwasher operation from producing a relative movement between said tub sidewalls and said roller mounting assembly means, thereby preventing cold flow enlargement of tub mounting bores and loss of seal integrity.
 2. The dishwasher of claim 1 wherein the rearward portions of said tub sidewalls converge rearwardly and merge with the rear tub wall at locations outside the parallel path of upper track movement.
 3. The dishwasher of claim 1 wherein said upper rack supporting rollers include mounting flanges associated therewith and abutting said plastic tub sidewalls when said rollers are mounted on said securing means.
 4. The dishwasher of claim 3 including mounting collar channels abutting each of said leading and trailing edge portions of said legs outside said dishwasher tub and having said stressed securing means passing therethrough to give additional support to said legs and to said tub sidewall and to coact against said mounting flanges when said stressed securing means are passed therethrough in assembled relation. 